[PATCH 6.1 060/166] btrfs: fix iomap_begin length for nocow writes

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

From: Christoph Hellwig <hch@xxxxxx>

commit 7833b865953c8e62abc76a3261c04132b2fb69de upstream.

can_nocow_extent can reduce the len passed in, which needs to be
propagated to btrfs_dio_iomap_begin so that iomap does not submit
more data then is mapped.

This problems exists since the btrfs_get_blocks_direct helper was added
in commit c5794e51784a ("btrfs: Factor out write portion of
btrfs_get_blocks_direct"), but the ordered_extent splitting added in
commit b73a6fd1b1ef ("btrfs: split partial dio bios before submit")
added a WARN_ON that made a syzkaller test fail.

Reported-by: syzbot+ee90502d5c8fd1d0dd93@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: c5794e51784a ("btrfs: Factor out write portion of btrfs_get_blocks_direct")
CC: stable@xxxxxxxxxxxxxxx # 6.1+
Tested-by: syzbot+ee90502d5c8fd1d0dd93@xxxxxxxxxxxxxxxxxxxxxxxxx
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/btrfs/inode.c |   18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7387,7 +7387,7 @@ static struct extent_map *create_io_em(s
 static int btrfs_get_blocks_direct_write(struct extent_map **map,
 					 struct inode *inode,
 					 struct btrfs_dio_data *dio_data,
-					 u64 start, u64 len,
+					 u64 start, u64 *lenp,
 					 unsigned int iomap_flags)
 {
 	const bool nowait = (iomap_flags & IOMAP_NOWAIT);
@@ -7398,6 +7398,7 @@ static int btrfs_get_blocks_direct_write
 	struct btrfs_block_group *bg;
 	bool can_nocow = false;
 	bool space_reserved = false;
+	u64 len = *lenp;
 	u64 prev_len;
 	int ret = 0;
 
@@ -7468,15 +7469,19 @@ static int btrfs_get_blocks_direct_write
 		free_extent_map(em);
 		*map = NULL;
 
-		if (nowait)
-			return -EAGAIN;
+		if (nowait) {
+			ret = -EAGAIN;
+			goto out;
+		}
 
 		/*
 		 * If we could not allocate data space before locking the file
 		 * range and we can't do a NOCOW write, then we have to fail.
 		 */
-		if (!dio_data->data_space_reserved)
-			return -ENOSPC;
+		if (!dio_data->data_space_reserved) {
+			ret = -ENOSPC;
+			goto out;
+		}
 
 		/*
 		 * We have to COW and we have already reserved data space before,
@@ -7517,6 +7522,7 @@ out:
 		btrfs_delalloc_release_extents(BTRFS_I(inode), len);
 		btrfs_delalloc_release_metadata(BTRFS_I(inode), len, true);
 	}
+	*lenp = len;
 	return ret;
 }
 
@@ -7693,7 +7699,7 @@ static int btrfs_dio_iomap_begin(struct
 
 	if (write) {
 		ret = btrfs_get_blocks_direct_write(&em, inode, dio_data,
-						    start, len, flags);
+						    start, &len, flags);
 		if (ret < 0)
 			goto unlock_err;
 		unlock_extents = true;